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Users satisfaction towards reading English newspapers has been a topic of interest in the literature. Studies have examined various factors that impact Users satisfaction, such as perceived usefulness, ease of use, content quality, trust, perceived value, brand equity, and demographics. For example, research has shown that factors like age, gender, and education level can influence satisfaction with English newspapers in India, while perceived value and satisfaction are significant predictors of loyalty in Korea. In Pakistan, trust and perceived value were found to impact Users satisfaction with English newspapers. Additionally, studies have explored Users satisfaction with online English newspaper services, finding that perceived usefulness, ease of use, and content quality are significant predictors of satisfaction. Overall, the literature suggests that multiple factors can impact Users satisfaction towards reading English newspapers, and understanding these factors can provide insights for improving newspaper services and increasing reader loyalty.

The low-frequency radio telescope of the Square Kilometre Array (SKA) is being built by the international radio astronomical community to (i) have orders of magnitude higher sensitivity and (ii) be able to map the sky several hundred times faster, than any other existing facilities over the frequency range of 50 - 350 MHz. The sensitivity of a radio telescope array is in general, dependent upon the number of electromagnetic sensors used to receive the sky signal. The total number of them is further constrained by the effects of mutual coupling between the sensor elements, allowable grating lobes in their radiation patterns, etc. The operating frequency band is governed by the desired spatial and spectral responses, acceptable sidelobe and backlobe levels, radiation efficiency, polarization purity and calibratability of sensors' response. This paper presents a brief review of several broadband antennas considered as potential candidates by various engineering groups across the globe, for the low-frequency radio telescope of SKA covering the frequency range of 50 - 350 MHz, on the basis of their suitability for conducting primary scientific objectives., Comment: 14 pages, 33 figures, JoAA - Special issue on the SKA (2023) - Accepted for publication

We present the pulse arrival times and high-precision dispersion measure estimates for 14 millisecond pulsars observed simultaneously in the 300-500 MHz and 1260-1460 MHz frequency bands using the upgraded Giant Metrewave Radio Telescope (uGMRT). The data spans over a baseline of 3.5 years (2018-2021), and is the first official data release made available by the Indian Pulsar Timing Array collaboration. This data release presents a unique opportunity for investigating the interstellar medium effects at low radio frequencies and their impact on the timing precision of pulsar timing array experiments. In addition to the dispersion measure time series and pulse arrival times obtained using both narrowband and wideband timing techniques, we also present the dispersion measure structure function analysis for selected pulsars. Our ongoing investigations regarding the frequency dependence of dispersion measures have been discussed. Based on the preliminary analysis for five millisecond pulsars, we do not find any conclusive evidence of chromaticity in dispersion measures. Data from regular simultaneous two-frequency observations are presented for the first time in this work. This distinctive feature leads us to the highest precision dispersion measure estimates obtained so far for a subset of our sample. Simultaneous multi-band uGMRT observations in Band 3 and Band 5 are crucial for high-precision dispersion measure estimation and for the prospect of expanding the overall frequency coverage upon the combination of data from the various Pulsar Timing Array consortia in the near future. Parts of the data presented in this work are expected to be incorporated into the upcoming third data release of the International Pulsar Timing Array., 23 pages, 21 figures, 3 tables. Published in PASA

Under Chandrayaan - II mission, simulation studies on lunar terrain were required for evaluation of the performance of rover and lander. In order to carry out mobility tests of a rover, it was required to prepare a lunar terrain testbed, which required a large quantity of lunar soil to represent the terrain conditions of the Moon. Under such compelling circumstances, U R Rao Satellite Centre (URSC), Indian Space Research Organization (ISRO), Bangalore, India has decided to manufacture indigenously lunar highland soil simulant, which can represent bulk chemistry, mineralogy and geomechanical properties of actual lunar highland soils brought by Apollo-16 mission of USA. This paper presents the process of manufacturing new lunar highland soil simulant (LSS-ISAC-1) and its various geomechanical properties such as cohesive modulus of deformation, frictional modulus of deformation, sinkage exponent, cohesion stress, angle of internal friction, shear deformation modulus and bulk density. The same were compared with the properties of actual lunar highland soil brought to the Earth by the Apollo-16. This new lunar highland soil simulant is being used for all qualifying tests required to be performed for the indigenously developed rover and the lander of the Chandrayaan mission.

High-precision measurements of the pulsar dispersion measure (DM) are possible using telescopes with low-frequency wideband receivers. We present an initial study of the application of the wideband timing technique, which can simultaneously measure the pulsar times of arrival (ToAs) and DMs, for a set of five pulsars observed with the upgraded Giant Metrewave Radio Telescope (uGMRT) as part of the Indian Pulsar Timing Array (InPTA) campaign. We have used the observations with the 300-500 MHz band of the uGMRT for this purpose. We obtain high precision in DM measurements with precisions of the order 10^{-6}cm^{-3}pc. The ToAs obtained have sub-{\mu}s precision and the root-mean-square of the post-fit ToA residuals are in the sub-{\mu}s range. We find that the uncertainties in the DMs and ToAs obtained with this wideband technique, applied to low-frequency data, are consistent with the results obtained with traditional pulsar timing techniques and comparable to high-frequency results from other PTAs. This work opens up an interesting possibility of using low-frequency wideband observations for precision pulsar timing and gravitational wave detection with similar precision as high-frequency observations used conventionally., Comment: Accepted for publication in MNRAS

Understanding the behavior of lunar regolith is important for designing the in-situ test equipment and building structures on the moon for the futuristic moon colonization. The Apollo missions brought back a small quantity of lunar soil to earth to assess the geotechnical properties of the lunar soil. However, it is essential to develop a lunar soil simulant (LSS) that is inexpensive and produced in large quantities to fulfill the extended research on lunar regolith. This paper presents the physical properties like specific gravity, particle size distribution, relative densities, etc., of a newly developed lunar soil simulant (LSS) for Chandrayaan missions. The triaxial test was conducted on the LSS at different confining pressures to discuss the influence of confining pressure on the stress–strain behavior of the LSS. The cyclic triaxial test was performed to find the dynamic properties like shear modulus, damping ratio, bulk modulus, and Poisson’s ratio of the LSS. The results were compared with the lunar soil Apollo 16 and simulants like GRC-3 and JSC-1A. The results evidence that the new LSS has similar properties of the lunar soil and can be used for future extended research about the lunar regolith.

The Stability of the superstructure of any building and its response against vibrations are completely dependent upon foundation systems adopted. The analysis and design of a foundation system with respect to ground motion and vibration relies on the dynamic properties of the soil. Therefore, the characterization of dynamic soil properties like shear modulus, damping ratio, and Poisson’s ratio is essential for the safe design of foundation systems. Dynamic characterization of geotechnical properties of lunar soil is essential for the design of rovers and other Space exploration vehicles apart from the in situ resource utilization (ISRU) on the Moon. The futuristic Moon colonization also needs to build different lunar infrastructure facilities on the Moon. The foundation systems of these lunar structures are expected to encounter various types of vibrations due to moonquakes. Therefore, it is imperative to evaluate the dynamic properties of the lunar soil against the moonquake induced vibrations. This paper explains the characterization of the dynamic properties of the lunar soil simulant (LSS-ISAC-1). The cyclic triaxial tests and bender element tests were performed to determine the shear modulus, damping ratio, and Poisson’s ratio of the lunar soil simulant

Indian Space Research Organization (ISRO) planned the Chandrayaan missions 2 and 3 to explore the South Polar Region of the Moon, which is believed to consist of lunar highland soil. As a part of its moon-landing mission, it is necessary to prepare a “lunar surface terrain testbed” so that the lander and rover could be tested under simulated conditions. This has resulted in a requirement of around 50 tons of lunar soil simulant, which can match with actual lunar highland soil with respect to chemical/mineralogical composition, particle size distribution, and some selected geomechanical properties, including the trafficability parameters, as reported in the literature. Though earlier, some countries (like USA, China, and Canada) have produced limited quantities of lunar highland soil simulants (LHSS), as reported in the literature, there was a compelling need to indigenously manufacture a large amount of lunar soil simulant (LSS) under the policy of “MAKE IN INDIA”. This technical note explains the development of a new lunar highland soil simulant LSS-ISAC-1 (that is jointly invented by ISRO Satellite Centre (ISAC) along with Periyar University, Salem and National Institute of Technology, Trichy—Tamilnadu) and its engineering properties, which was manufactured in a large quantity using the natural terrestrial anorthosite rocks. Furthermore, this note also highlights the futuristic research areas, where this soil simulant can be advantageously used for further research and development works.

The Regenerative Storage Heater (RSH) is employed in Hypersonic Wind Tunnel (HWT) to prevent liquefaction of air during expansion in the high Mach number nozzles. Design of RSH is a multi-variable iterative process depends on the total energy required, the exit temperature of the air and the duration of blowdown. Arriving at the optimal design of RSH is essential as it has a high economic impact. After arriving at the design, evaluation of the performance of RSH for all the possible operating conditions prior to manufacturing is critical. The current research work addresses the challenge by evolving a mathematical framework using multi-objective optimization functions. MATLAB based integrated Graphical User Interface (GUI) has been developed to study the design and analysis simultaneously. This GUI framework defines the inputs, constraints and the parameters of optimal design for the RSH and calculates the optimal size of the RSH. The paper presents the details of the size of the heater for multi hole multi brick configuration in the RSH for a given input conditions of a Mach 5.0 wind tunnel heater case. The current research also presents the details of the temperature profiles of the bed during heating and blowdown cycles. Finally, framework has been used to design the heater for one of the known published data. It is found that the predicted performance of RSH is in good agreement with the published data. This has established the accuracy of the developed framework.

The engineering properties (shear strength and compressibility) of lunar soils influence the design of landers, rovers, and their mobility behavior on the lunar surface. Assessing such properties is important for any lunar-based studies, and it is usually being determined by using suitable lunar soil simulants. This paper explains the shear strength parameters, stress-strain relationships, and volume change behavior of the newly developed lunar highland soil simulant (LSS-ISAC-1), apart from particle size distribution, which have a profound influence on the engineering behavior. In addition, to the above, other engineering properties such as critical state of the angle of internal friction, dilatancy angle, Young's modulus, Poisson's ratio, internal erodibility, small-strain shear wave velocity, and shear modulus have also been evaluated and presented. Mohr-Coulomb and friction-dilatancy theories are considered as a base for the analysis with the use of statistical predictive equations. The relative density and confining pressures are used as functions in the predictive equation to assess the behavior of the LSS-ISAC-1. The comparison of properties with the actual lunar highland soil samples of the Apollo 16 mission reveals a reasonable similarity of LSS-ISAC-1 with the lunar highland soils.

Indian Government has set ambitious targets for solar PV of 100 GW under the National Solar Mission by the year 2022. The installed capacity has already reached 28GW as on March 2019. The inverter is one of the main components of solar PV conversion system. Due to varying irradiation profile in India, the inverters used in Solar PV applications are subjected to varying levels of DC input power. At present two weighted average methods namely EURO and California Energy Commission (CEC) efficiency formulae have been used by inverter manufacturers worldwide to evaluate the performance of inverters. These methods are representative of inverter efficiencies at Europe and California, thus cannot be suitable benchmarks to find out the conversion efficiency of the inverters in other locations. The present research and this paper proposes about introducing new weighting factors for calculation of inverter efficiency as per irradiation profile in India. As a step 1, for computing the weighting factors the data from Solar Radiation Resource Assessment (SRRA) stations implemented by National Institute Of Wind Energy (NIWE) is used and are categorized into five climatic zones. In step 2 validation of three inverters were done by calculating the weighted average efficiency of these inverters operating in all the climatic zones by considering the new weighting factors. Further in step 3, it was cross-compared with the standard values of EURO and CEC efficiency. In step 4, the modelled overall weighted average efficiency is subsequently compared with the actual measured weighted average efficiency. The measured DC Energy and AC Energy of the plant was used for this purpose. The proposed approach has been generalized to consider the irradiation profile of a particular location for calculating the inverter efficiency and hence it can provide significant insights related to the performance of inverters for the solar projects.

The Indian Space Research Organization (ISRO) has planned to explore the possibility of soft-land the lander/rover on the highland area of the Moon. The rover mobility and interaction studies under the terrain condition of the Moon need a large quantity of lunar soil simulant. This study presents the development of a new novel lunar highland soil simulant (LSS-ISAC-1) by using natural terrain anorthosite rock fragments without the addition of any chemicals or other minerals, etc. This study presents the development of a new lunar highland soil simulant (LSS-ISAC-1) representing the lunar highland soils. The geotechnical properties such as particle size distribution, specific gravity, shear strength, compaction, and compressibility of the LSS-ISAC-1 have been determined and compared with the Apollo 16 lunar highland soil properties and other available highland simulants. The bulk chemistry and particle morphology of the simulant were identified by performing X-ray Fluorescence Spectrometer Tests (XRF) and scanning electron microscopy (SEM) analysis. The comparison shows that the bulk chemistry, mineralogy, and geotechnical properties of the LSS-ISAC-1 are representative of the Apollo 16 lunar highland soil and comparatively match with the lunar highland simulants.

Detection of the epoch of reionization H i signal requires a precise understanding of the intervening galaxies and AGN, both for instrumental calibration and foreground removal. We present a catalogue of 7394 extragalactic sources at 182 MHz detected in the RA = 0 field of the Murchison Widefield Array Epoch of Reionization observation programme. Motivated by unprecedented requirements for precision and reliability we develop new methods for source finding and selection. We apply machine learning methods to self-consistently classify the relative reliability of 9490 source candidates. A subset of 7466 are selected based on reliability class and signal-to-noise ratio criteria. These are statistically cross-matched to four other radio surveys using both position and flux density information. We find 7369 sources to have confident matches, including 90 partially resolved sources that split into a total of 192 sub-components. An additional 25 unmatched sources are included as new radio detections. The catalogue sources have a median spectral index of −0.85. Spectral flattening is seen towards lower frequencies with a median of −0.71 predicted at 182 MHz. The astrometric error is 7 arcsec compared to a 2.3 arcmin beam FWHM. The resulting catalogue covers ∼1400 deg² and is complete to approximately 80 mJy within half beam power. This provides the most reliable discrete source sky model available to date in the MWA EoR0 field for precision foreground subtraction., National Science Foundation (U.S.) (AST-0847753), National Science Foundation (U.S.) (AST-1410484), National Science Foundation (U.S.) (AST-1506024)

Finite Impulse response filter is one of the fundamental devices in all digital processing system. Nowadays area efficient parallel FIR filter is most preferred in digital signal processing systems. In this research paper, such a filter is designed using carry select adder. For the reliable operation of filter, it must be protected. Filter protection is done using fault tolerant methods. Here the filtering effect of digital filter is analyzed by single error correction code. The experimental results show that the FIR filter designed is effective.

This research paper introduces a confidence measure scheme to detect the vehicles under various natural environmental scenes. In elaborate city traffic scenes, the GMM (Gaussian mixture model) is designed for vehicle detection. Using different climatic conditions, the experiments are conducted by Gaussian mixture model with parameter measurement. The measured parameters are compared with adaptive background learning algorithm. The experimental results shows that GMM excels adaptive method by staying the background model being uncontaminated from slow-relocating or briefly stopped cars.

In small wind turbine generator systems (SWTG), the most commonly encountered issue is the fluctuations in the power developed due to the uneven wind velocities. Hence it is preferred not to feed this power to any direct stand-alone systems or to loads continuously. To overcome this issue, the power produced is stored in a battery and fed to the load. Here in this proposed system, the wind turbine is directly connected to a load along with an electrolyser. If the source is constant or fluctuates, the excess power from the turbine has to be accommodated by the electrolyser. Hence an electrolyser is connected to which the excess power from SWTG is re-directed for the production of H 2 and could be stored. The stored H 2 can be used for variety of applications. The major focus of this case arises in case of waste treatment plants and stand-alone captive power generation plants where excess or off peak periods are available. Here the main challenge is to control the power flow along with the simultaneous switching of the converter. The produced hydrogen gas can be stored as metal hydrides which is one of the safest and advanced technologies of hydrogen storage.

Detection of the fluctuations in 21 cm line emission from neutral hydrogen during the Epoch of Reionization in thousand hour integrations poses stringent requirements on calibration and image quality, both of which necessitate accurate primary beam models. The Murchison Widefield Array (MWA) uses phased array antenna elements which maximize collecting area at the cost of complexity. To quantify their performance, we have developed a novel beam measurement system using the 137 MHz ORBCOMM satellite constellation and a reference dipole antenna. Using power ratio measurements, we measure the {\it in situ} beampattern of the MWA antenna tile relative to that of the reference antenna, canceling the variation of satellite flux or polarization with time. We employ angular averaging to mitigate multipath effects (ground scattering), and assess environmental systematics with a null experiment in which the MWA tile is replaced with a second reference dipole. We achieve beam measurements over 30 dB dynamic range in beam sensitivity over a large field of view (65\% of the visible sky), far wider and deeper than drift scans through astronomical sources allow. We verify an analytic model of the MWA tile at this frequency within a few percent statistical scatter within the full width at half maximum. Towards the edges of the main lobe and in the sidelobes, we measure tens of percent systematic deviations. We compare these errors with those expected from known beamforming errors.

Ionization of the Earth's atmosphere by sunlight forms a complex, multi-layered plasma environment within the Earth's magnetosphere, the innermost layers being the ionosphere and plasmasphere. The plasmasphere is believed to be embedded with cylindrical density structures (ducts) aligned along the Earth's magnetic field, but direct evidence for these remains scarce. Here we report the first direct wide-angle observation of an extensive array of field-aligned ducts bridging the upper ionosphere and inner plasmasphere, using a novel ground-based imaging technique. We establish their heights and motions by feature-tracking and parallax analysis. The structures are strikingly organized, appearing as regularly-spaced, alternating tubes of overdensities and underdensities strongly aligned with the Earth's magnetic field. These findings represent the first direct visual evidence for the existence of such structures., Accepted for publication in Geophysical Research Letters

An improvement in performance of hybrid solar system with use of liquid metal alloy GaInSn as a coolant has been demonstrated in this study. The performance of hybrid system using GaInSn, water, and air as coolants under different operating conditions such as ambient temperature, different inlet velocities of fluid, solar irradiations is analyzed using simulation software ANSYS and the results obtained are validated using experiments. The results obtained from simulations and experiments are used for determining important performance criteria such as electrical efficiency, thermal efficiency, and exergy efficiency. The exergy, thermal, and electrical efficiencies were found to be at least 11%, 12%, and 12% higher for hybrid system using GaInSn as a coolant when compared to hybrid systems using air and water as coolants, respectively.

Many astronomical sources produce transient phenomena at radio frequencies, but the transient sky at low frequencies (, 16 pages, 14 figures, accepted to AJ

Objectives: The main objective of the paper is to perform a repowering assessment of an old wind farm consisting of 2 bladed turbines located at Gudimangalam near Coimbatore in Tamil Nadu which is a good wind potential site. Methods/Statistical Analysis: Repowering refers to the replacement of first generation small capacity wind turbines with modern multi megawatt wind turbines that can produce more energy than before from the same site. Technical analysis of the site is done using WAsP software with the help of wind data collected from a met mast at the site and includes the calculation of Net Annual Energy Production and Wake losses. Net Annual Energy Production and Wake losses are the primary indicators for selecting the best options for repowering. The option selected is further supported by calculating the economic performance indices. The total repowering has been accomplished through partial repowering executed in three stages. Partial repowering refers to the replacement of only few of the turbines from the existing wind farm rather than replacing the whole farm. The economic feasibility of every repowering option has been studied based on the calculation of the economic performance indices like ALCoG, Payback Period and IRR. Findings: The study mainly results in framing a procedure for performing total repowering for any site through the optimization of best possible partial repowering options. The existing site comprises 18 turbines of 450 kW rating and is having a net AEP of 14.5 GWh with a wake loss of 3.82%. The Plant Load Factor (PLF) is obtained to be 20.44%. The best possible total repowering option is found to be producing a net AEP of 65.287 GWh with a wake loss of 2.36% and included 9 Suzlon S95 2.1 MW turbines which are four times the AEP of the existing farm. The three stages of partial repowering also include replacement of 6 old turbines by 3 new turbines in each stage. Finally the total repowering is reached through the execution of partial repowering options in three stages and it results in close proximity to the best possible total repowering option in both technical and economic aspects. The final repowering eventually attained results in a net AEP of 65.28 GWh with a wake loss of 2.36% which is the exact match of the best possible total repowering option found in the beginning. The total repowering also leads to an improvement in PLF i.e. almost doubles the PLF to 39.42%. Application/Improvements: This procedure can be very useful where the initial investment is an important factor. The study infers that performing total repowering through optimization process is more beneficial than performing partial repowering randomly.

We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple, independent, data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregrounds., Comment: accepted to ApJ

GLEAM, the GaLactic and Extragalactic All-sky MWA survey, is a survey of the entire radio sky south of declination +25 deg at frequencies between 72 and 231 MHz, made with the Murchison Widefield Array (MWA) using a drift scan method that makes efficient use of the MWA's very large field-of-view. We present the observation details, imaging strategies and theoretical sensitivity for GLEAM. The survey ran for two years, the first year using 40 kHz frequency resolution and 0.5 s time resolution; the second year using 10 kHz frequency resolution and 2 s time resolution. The resulting image resolution and sensitivity depends on observing frequency, sky pointing and image weighting scheme. At 154 MHz the image resolution is approximately 2.5 x 2.2/cos(DEC+26.7) arcmin with sensitivity to structures up to ~10 deg in angular size. We provide tables to calculate the expected thermal noise for GLEAM mosaics depending on pointing and frequency and discuss limitations to achieving theoretical noise in Stokes I images. We discuss challenges, and their solutions, that arise for GLEAM including ionospheric effects on source positions and linearly polarised emission, and the instrumental polarisation effects inherent to the MWA's primary beam., 17 pages, 7 Figures, 4 tables. Accepted for publication in the Publications of the Astronomical Society of Australia (PASA)

The science cases for incorporating high time resolution capabilities into modern radio telescopes are as numerous as they are compelling. Science targets range from exotic sources such as pulsars, to our Sun, to recently detected possible extragalactic bursts of radio emission, the so-called fast radio bursts (FRBs). Originally conceived purely as an imaging telescope, the initial design of the Murchison Widefield Array (MWA) did not include the ability to access high time and frequency resolution voltage data. However, the flexibility of the MWA's software correlator allowed an off-the-shelf solution for adding this capability. This paper describes the system that records the 100 micro-second and 10 kHz resolution voltage data from the MWA. Example science applications, where this capability is critical, are presented, as well as accompanying commissioning results from this mode to demonstrate verification., Comment: 9 pages, 6 figures, 1 table. Accepted for publication in PASA

The Murchison Widefield Array (MWA) is a new low-frequency interferometric radio telescope built in Western Australia at one of the locations of the future Square Kilometre Array (SKA). We describe the automated radio-frequency interference (RFI) detection strategy implemented for the MWA, which is based on the AOFlagger platform, and present 72-231-MHz RFI statistics from 10 observing nights. RFI detection removes 1.1% of the data. RFI from digital TV (DTV) is observed 3% of the time due to occasional ionospheric or atmospheric propagation. After RFI detection and excision, almost all data can be calibrated and imaged without further RFI mitigation efforts, including observations within the FM and DTV bands. The results are compared to a previously published Low-Frequency Array (LOFAR) RFI survey. The remote location of the MWA results in a substantially cleaner RFI environment compared to LOFAR's radio environment, but adequate detection of RFI is still required before data can be analysed. We include specific recommendations designed to make the SKA more robust to RFI, including: the availability of sufficient computing power for RFI detection; accounting for RFI in the receiver design; a smooth band-pass response; and the capability of RFI detection at high time and frequency resolution (second and kHz-scale respectively)., Comment: Accepted for publication in PASA

Detection of 21~cm emission of HI from the epoch of reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the HI signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic "pitchfork" signature on the "foreground wedge" in Fourier delay space. Based on these results, we propose that selective down-weighting of data based on antenna spacing and time can mitigate foreground contamination substantially by a factor ~100 with negligible loss of sensitivity., Published in ApJ

We confirm our recent prediction of the "pitchfork" foreground signature in power spectra of high-redshift 21 cm measurements where the interferometer is sensitive to large-scale structure on all baselines. This is due to the inherent response of a wide-field instrument and is characterized by enhanced power from foreground emission in Fourier modes adjacent to those considered to be the most sensitive to the cosmological H I signal. In our recent paper, many signatures from the simulation that predicted this feature were validated against Murchison Widefield Array (MWA) data, but this key pitchfork signature was close to the noise level. In this paper, we improve the data sensitivity through the coherent averaging of 12 independent snapshots with identical instrument settings and provide the first confirmation of the prediction with a signal-to-noise ratio > 10. This wide-field effect can be mitigated by careful antenna designs that suppress sensitivity near the horizon. Simple models for antenna apertures that have been proposed for future instruments such as the Hydrogen Epoch of Reionization Array and the Square Kilometre Array indicate they should suppress foreground leakage from the pitchfork by ~40 dB relative to the MWA and significantly increase the likelihood of cosmological signal detection in these critical Fourier modes in the three-dimensional power spectrum., Accepted for publication in ApJ Letters, 6 pages, 2 figures

Production rates of cosmogenic nuclides at the earth's surface are controlled by the intensity of energetic cosmic-ray nucleons, which changes rapidly with elevation. An incomplete knowledge of how nucleon fluxes vary with elevation remains a major obstacle to utilizing cosmogenic nuclides as geochronometers in applications requiring highly accurate ages. One problem is that attenuation characteristics depend on nucleon energy. Measurements of high-energy (> 50 MeV) nucleon fluxes tend to give shorter attenuation lengths than low-energy (

Using the new wideband capabilities of the Australia Telescope Compact Array (ATCA), we obtain spectra for PKS 1718-649, a well-known gigahertz-peaked spectrum radio source. The observations, between approximately 1 and 10 GHz over three epochs spanning approximately 21 months, reveal variability both above the spectral peak at ~3 GHz and below the peak. The combination of the low and high frequency variability cannot be easily explained using a single absorption mechanism, such as free-free absorption or synchrotron self-absorption. We find that the PKS 1718-649 spectrum and its variability are best explained by variations in the free-free optical depth on our line-of-sight to the radio source at low frequencies (below the spectral peak) and the adiabatic expansion of the radio source itself at high frequencies (above the spectral peak). The optical depth variations are found to be plausible when X-ray continuum absorption variability seen in samples of Active Galactic Nuclei is considered. We find that the cause of the peaked spectrum in PKS 1718-649 is most likely due to free-free absorption. In agreement with previous studies, we find that the spectrum at each epoch of observation is best fit by a free-free absorption model characterised by a power-law distribution of free-free absorbing clouds. This agreement is extended to frequencies below the 1 GHz lower limit of the ATCA by considering new observations with Parkes at 725 MHz and 199 MHz observations with the newly operational Murchison Widefield Array. These lower frequency observations argue against families of absorption models (both free-free and synchrotron self-absorption) that are based on simple homogenous structures., Accepted for publication in The Astronomical Journal

Wonders of the night sky developed curiously to the ancient civilization and paved way to the development of an oldest branch of knowledge, Astronomy. Today it has developed to be rich field in science. Astronomy is much different from many other science fields. ? It deals with remote subjects, unimaginable magnitude distances, sizes and time. The conventional optical telescope could not reveal vast majority of objects in the sky. Apart from light there are other invisible radiations reaching the Earth from the celestial objects. People started exploring both ends of the electromagnetic spectrum. Ever since World War II, astronomers are exploring the radio sky, by using Radio Telescopes. It became a new branch of study, the Radio Astronomy. Interesting fundamental discoveries and the inquisitive nature of the problems developed curiosity for future explorations in this field. The celestial radio signals reaching us are extremely week. It is required to develop sophisticated tools and powerful techniques to aid radio astronomy observations. Today Radio Astronomy has developed to be a highly interdisciplinary field with connections to various fields of science and engineering.

The Sun has remained a difficult source to image for radio telescopes, especially at the low radio frequencies. Its morphologically complex emission features span a large range of angular scales, emission mechanisms involved and brightness temperatures. In addition, time and frequency synthesis, the key tool used by most radio interferometers to build up information about the source being imaged is not effective for solar imaging, because many of the features of interest are short lived and change dramatically over small fractional bandwidths. Building on the advances in radio frequency technology, digital signal processing and computing, the kind of instruments needed to simultaneously capture the evolution of solar emission in time, frequency, morphology and polarization over a large spectral span with the requisite imaging fidelity, and time and frequency resolution have only recently begun to appear. Of this class of instruments, the Murchison Widefield Array (MWA) is best suited for solar observations. The MWA has now entered a routine observing phase and here we present some early examples from MWA observations., 4 pages, 3 figures, submitted for the 31st URSI General Assembly and Scientific Symposium, to be held in Bejing, China from 16-23, August, 2014